Skip to main content
Version: 5.x

How-to: FOR

Example 1​

Task​

We have a list of books with titles.

CLASS Book 'Book';
name 'Name' = DATA ISTRING[50] (Book);

FORM books 'Books'
    OBJECTS b = Book
    PROPERTIES(b) name, NEW, DELETE
;

NAVIGATOR {
    NEW books;
}

We need to find all the books containing a given line and display a message with their names and internal codes.

Task​

findNemo 'Find book' ()  {
    FOR isSubstring(name(Book b), 'Nemo') DO {
        MESSAGE 'Found book ' + name (b) + ' with internal code ' + b;
    }
}
EXTEND FORM books
    PROPERTIES() findNemo
;

Use the isSubstring property (defined in the Utils system module) to identify whether a given line contains another line.

Example 2​

Task​

Similar to Example 1.

We need to create an action that creates 100 new books with certain titles.

Solution​

add100Books 'Add 100 books' ()  {
    // Option 1
    FOR iterate(INTEGER i, 1, 100) NEW b = Book DO {
        name(b) <- 'Book ' + i;
    }

    // Option 2
    FOR iterate(INTEGER i, 1, 100) DO {
        NEW b = Book {
            name(b) <- 'Book ' + i;
        }
    }
}

EXTEND FORM books
    PROPERTIES() add100Books
;

Both these implementations will provide the same result.

To solve this task, use the iterate property (defined in the Utils system module) which returns TRUE for all integers in the range.

Example 3​

Task​

Similar to Example 1, but with the order logic. Each order contains lines where books and discount prices are specified.

CLASS Order 'Order';

CLASS OrderDetail 'Order line';
order 'Order' = DATA Order (OrderDetail) NONULL DELETE;
book 'Book' = DATA Book (OrderDetail);
nameBook 'Book' (OrderDetail d) = name(book(d));

price 'Price' = DATA NUMERIC[14,2] (OrderDetail);

discount 'Discount, %' = DATA NUMERIC[8,2] (OrderDetail);
discountPrice 'Discount price' = DATA NUMERIC[14,2] (OrderDetail);

We need to create an action that applies a discount to all the lines with prices above 100.

Solution​

makeDiscount 'Make discount' (Order o)  {
    // Option 1
    FOR order(OrderDetail d) == o AND price(d) > 100 DO {
        discount(d) <- 10;
        discountPrice(d) <- price(d) * (100.0 - discount(d)) / 100.0;
    }

    // Option 2
    discount(OrderDetail d) <- 10 WHERE order(d) == o AND price(d) > 100;
    discountPrice(OrderDetail d) <- price(d) * (100.0 - discount(d)) / 100.0 WHERE order(d) == o AND price(d) > 100;
}

Both these implementations will provide the same result.

Example 4​

Task​

Similar to Example 3, but a default price was added for each book.

price 'Price' = DATA NUMERIC[14,2] (Book);

We need to create an action that adds all the books with prices above 100 to the order.

Solution​

addSelectedBooks 'Add marked books' (Order o)  {
    // Option 1
    FOR price(Book b) > 100 NEW d = OrderDetail DO {
        order(d) <- o;
        book(d) <- b;
        price(d) <- price(b);
    }

    // Option 2
    FOR price(Book b) == NUMERIC[14,2] p AND p > 100 NEW d = OrderDetail DO {
        order(d) <- o;
        book(d) <- b;
        price(d) <- p;
    }
}

Both these implementations will provide the same result.